1. Field of the Invention
The present invention relates to methods of making radar absorber structures, and more particularly to a method for forming absorber structures having reduced weight without compromised structural properties.
2. Description of the Related Art
The use of open-cell foam substrates having a conductive filler to form light-weight broadband microwave absorbers is known. However, such absorbers suffer from a variety of drawbacks.
For one thing, repeated flexure of the absorbers results in reduction of the elasticity, with resultant failure, of the foam, as well as failure or other deleterious effects in the conductive filler. In many situations, the foam absorbers are rendered defective due to improper distribution of the conductive material in the foam. In other situations, the weight of the absorber and conductive filler exceeds the permissible limits of the anticipated application.
U.S. Pat. No. 5,192,810 issued Mar. 9, 1993 to Hill discloses a method and apparatus for manufacturing dimpled structures from elastic cloth. The method permits forming complex polyimide foam shapes through the steps of impregnating a low density, open cell, reticulated foam with polyimide foam precursor, placing the combination in a mold, closing the mold, then heating the assembly to the foaming and curing temperatures of the precursor. As the powdered precursor expands, it spreads throughout the reticulated foam producing a product having substantially uniform density and polyimide foam characteristics. If desired, the reticulated foam can be removed from the product by using a material that outgasses and boils away at polyimide processing temperatures. Radar absorbing materials may be incorporated in the reticulated foam so that the final product will have uniformly distributed radar absorbing components with the desirable high temperature resistance and other properties of polyimide foams.
U.S. Pat. No. 5,845,877 to Justice et al. and issued on Dec. 8, 1998 discloses a sealing assembly for reducing the gap between an aircraft's movable flight control member and adjacent structures. The flight control member and adjacent structures have external surfaces and side surfaces facing each other. First and second flexible bulb seals are mounted on the periphery of the side surface of both the flight control member and the adjacent structure forming an extension of the external surface of both. Each bulb seal includes a compressible foam bulk absorber core. A first sheet of dielectric material is bonded to the bottom surface of the core. A second sheet of flexible resistive material is bonded to the top, and sides of the core. A third sheet of flexible magnetic radar absorbing material is bonded to the second sheet. A fourth sheet of flexible abrasion resistant material is bonded over the third sheet.
Against this background of known technology, the applicant has developed a novel method for forming a low density closed cell foam filled reticulated absorber having significant weight reduction properties and which can be shaped and cured to form simple or complex components at low cost and with little difficulty, while overcoming many of the deficiencies and drawbacks of similar absorbers currently known in the relevant technology